Memcache is a distributed object caching system and uses key-value for storing small data. Before you start calling Memcache code into PHP, you need to make sure that it is installed. That can be done using class_exists method in php. Once it is validated that the module is installed, you start with connecting to memcache server instance.

if (class_exists('Memcache')) {
  $cache = new Memcache();
  $cache->connect('localhost',11211);
}else {
  print "Not connected to cache server";
}

This will validate that Memcache php-drivers are installed and connect to memcache server instance running on localhost.

Memcache runs as a daemon and is called memcached

In the example above we only connected to a single instance, but you can also connect to multiple servers using

if (class_exists('Memcache')) {
  $cache = new Memcache();
  $cache->addServer('192.168.0.100',11211);
  $cache->addServer('192.168.0.101',11211);
}

Note that in this case unlike connect , there wont be any active connection until you try to store or fetch a value.

In caching there are three important operations that needs to be implemented

1. Store data : Add new data to memcached server
2. Get data : Fetch data from memcached server
3. Delete data : Delete already existing data from memcached server

Store data

$cache or memcached class object has a set method that takes in a key,value and time to save the value for (ttl).

$cache->set($key, $value, 0, $ttl);

Here $ttl or time to live is time in seconds that you want memcache to store the pair on server.

Get data

$cache or memcached class object has a get method that takes in a key and returns the corresponding value.

$value = $cache->get($key);

In case there is no value set for the key it will return null

Delete data